The present invention generally refers to the art of printing. It concerns a method for the manufacture or the decoration of shaped objects of which at least one surface is provided with a generally but not exclusively decorative pattern in relief. More especially, the invention relates to the application of said method to packages of all types and of all solid materials which are printable and generally provided in a two-dimensional form. This term designates any material whose thickness is smaller than its length and width by several orders of magnitude. Examples are textile materials in web form, paper and cardboard in webs, metal sheets, metal foils such as aluminum or tin foils, plastics foils, and combinations or compounds (laminates) of the cited materials. This list is not exhaustive.
It is well known to provide the surfaces of a two-dimensional material with relief portions or patterns. For example, the different methods of embossing may be applied in order to obtain these decorative or functional relief patterns.
However, embossing has the drawback, inter alia, that while a positive pattern is produced on the back of a two-dimensional material, the negative of that same pattern is simultaneously formed on the upper surface of said material.
Attempts have been made to eliminate the drawbacks of embossing by developing so-called "inflatable (expanding) inks". These are printing inks which form reliefs by expansion at precise and desired locations, i.e. where the ink has been applied, under the action of heat or of energetic radiation capable of heating the printing. The heated ink will permanently expand at the printed sites, thus producing the desired relief. The back of the printed two-dimensional material remains unaltered. This "embossing" method by inflatable or expanding inks is known for the manufacture of wallpaper, for example.
This relief expansion procedure is carried out preferably by continuously printing one or a plurality of inflatable inks onto the two-dimensional support according to the desired pattern, by drying the printing, passing the printed material through an oven at e.g. 180.degree. during or after drying, or otherwise applying the heat (e.g. by infrared radiation), and winding up the expanded support coming out from the oven.
However, serious problems arise when the printed and partially expanded support is wound up for a subsequent use, e.g., in the manufacture of packages. A tight winding cannot be obtained, and loosely wound rolls or bobbins are seriously deformed during stocking, transportation and handling, so as to become useless. Moreover, the relief is subject to mechanical abrasion.
As far as wallpaper is concerned, this problem is not important since this paper comes in quite short and thin rolls.